1. Field of the Invention
The present invention pertains to liquid crystal display (LCD) systems, and more particularly to improved two panel optical engines using simpler optical retarder for color display projection.
2. Description of the Prior Art
As earlier research projects in developing microdisplay systems using the liquid crystal display technologies were mostly for military and specialized applications with high performance requirements, the systems were generally configured without much concern for production costs. However, some of the configurations as developed earlier now become quite costly when the microdisplay systems are commercialized for high definition TVs and used as monitor for computers. One particular system is the simplified two panels display configurations while cost savings are achieved with two instead of three color display panels, the optical components used for color path separation and polarization modifications as disclosed by the conventional configurations are specially made thus unduly increases the production cost of such systems.
It is well known that the complexity of on-axis optical engines has hindered the development of cost-effective liquid crystal on silicon display devices for projection applications. The earliest developments were based on earlier reflective light valve efforts that were manufactured to high levels of performance at great cost for industrial and military uses. The more recent approaches have been for application in commercial display products such as data monitors and television receiving sets. While much of the earlier work remains relevant to background, improved solutions of lower cost have been sought.
The earliest attempts to solve this problem have required compromises. For example, in U.S. Pat. No. 4,500,172, a two-panel reflective display architecture is disclosed that is limited to modulated light of two primary colors displayed on a constant background of the third primary color. Two beams of polarized colored light, said two beams of light having different spectra, are directed onto one surface of a polarizing beamsplitter. The two reflective displays are arrayed on two remaining faces of the polarizing beamsplitter. The fourth port of the polarizing beamsplitter delivers the combined beams to a lens group for projection onto a viewing screen.
Later, Sharp et al disclose in PCT Application WO 00/7-376 a two-panel architecture requiring the use of color selective retarder stacks that separate linearly polarized light into orthogonal polarized beams of light based on the spectrum of the light. The orthogonally polarized beams of light are then separated by a polarizing beamsplitter (PBS) and directed onto the faces of two different microdisplays for image generation. The optical architecture therein is efficient and practical, but suffers in application because of the high cost and limited supply of the color selective retarder stacks.
For these reasons, there is still need and challenge in the art of microdisplay such as a two-panel liquid crystal on silicon (LCOS) display to provide improved system architecture and methods for polarization and color separation.